Reinforced flexible duct



Oct. 22, 1957 A. E. HEwlTT YRlazINFoRclazD FLEXIBLE DUCT Filed Aug. 24,1954 W/ WW i wm/ United States Patent C ice REINFoRcED FLEXIBLE DUCTAlvin E. Hewitt, Chanute, Kans., assignor to American AutolasticCorporation, Chanute, Kaus., a corporation of Kansas Application August24, 1954, Serial No. 451,907

7 Claims. (Cl. 13S-56) This invention relates toa flexible ductconstruction, and particularlyto a construction of a reinforced, exible,fabric duct in which the spiral reinforcing strand is firmly enclosedwithin the Wall of the duct. The invention relates more specifically toa duct construction in` which the completed duct is produced by spirallywrapping a tape on a mandrel, cementing or vulcanizing the edges to forma unitary structure.

The invention is illustrated by drawings which show in Figure l theoperation of winding the duct on a mandrel. Figures 2-6 show incross-sections one wall of the duct in five modifications to bedescribed hereinafter.

Heretofore in the manufacture of exibletducts it has been the practiceto wrap a sheet or a strip of fabric on the mandrel, then apply areinforcing strand to the out side if desired, and finally cover thereinforcing with an additional covering of tape or fabric strip. Thereinforcing is usually wire, to provide rigidity to the duct in a radialdirection while maintaining flexibility in a longitudinal direction.apply the reinforcing-spirally andlock the ends ofthe reinforcing wireto the wall of the duct. jIt has also been the practice to apply acement, for example, rubber cement, plastic, etc.,'to the fabric beforeapplying the final wrapping,'thereby.securing the `various elements intheir desired position. This method of construction has had thedisadvantage Vof leaving seams` on the surfaceof the duct:Y where theedges of fabric joined and these were usually fastened by sewing or bycementing. However they were fastened, the seamsA generally required anextra operation to protect them and prevent the wall of theduct openingalong the line of the seam. Also-the manufacture of ducts of thistypefhas required numerous operations, usually at least three operationsbeing necessary, including the primary winding of fabric, the winding ofthe'reinforcing wire and the final winding of overlying fabric or tapetohold the reinforcing wire in the proper position.

In another method of making ilexible ducting, the fabric tape was foldedover the reinforcing wire and wound into a tubular form by a headwhereby a set of rollers coiled the tape into a continuous duct `inwhich the seams we'reieither cementedvor sewed during the coilingoperation. The -resultingductewas not smooth internally, but presentedav succession of ridges and .valleys to the fluid stream-transportedtherein, much as does a corrugated tube. Y.

It is an object of this invention to reduce the number of operationsrequired in the manufacture of ducts of the reinforced flexible type,thereby reducing the cost of manufacture. Another object of theinvention is to provide a duct of the reinforced flexible type in whichno seams are apparent on the outside or the inside surfaces of the duct.

Another object of the invention is to provide a flexible duct with asmooth, cylindrical interior when extended, thereby providing maximumfluid carrying capacity with minimum turbulence. Previous methods ofduct manu- It has usually been the practice toV being employed in thecomposition'to effect rapid vul-.

Patented Oct. 22, 1957' facture have left ridges on the inside tointerfere seriously with flow of air thru theduct.

A further obiect of the invention is to make a sprally wound duct withcemented seams or laps without defects caused by separation of theseams. Ducts of this type haveheretofore not met the rigid requirementsof the aviation industry, owing to the hazard resulting from occasionalfailure of seams not properly cemented orvulcanized. The manner ofaccomplishing these objects will beshown in thefollowing description ofthe invention.

lReferring to the drawings, Figure 1 shows the manner. of wrapping theduct on the'mandrel 10. This is done by. applying to thel mandrel aVtape in which the reinforcing strand 11 is folded within a strip offabric 12, with the wire 11 at one edge of the tape. `This ismostconveniently done by applying` the tape to a rotating mandrel having thediameter of the desired duct. The tape with wire enfolded can be,prepared infadvance or the wire can be folded in the tape at thepointof winding on the mandrel.

Thevtape isapplied with suflcient tension to bind the windings firmlyagainst the mandrel, placing .the laps under compression to unite themwith a firm bond. Before winding, the tape is impregnated with asuitable adhesive, usually rubber or other elastomer, which not onlyseals the pores ofthe fabric, but also cements the successive windings-together. use cements of natural rubber or. syntheticrubber such asBuna-S, Buna-N, butyl, neoprene, lactoprene, Thiokol or siliconerubber(polysiloxane), etc. After the duct, is wound, applying the wrappingsunder tension,

` the entire assembly is vulcanized while under tension by heating inthe usual m'anner, for example,'in an auto; clave. In the caseaofrubber, either natural or synthetic,

vulcanization is usually accomplished by heating to va temperature ofabout 250-300 F., sulfur and accelerators canizatioin.` In the case ofcertain other elastomers, such as silicone, vulcanization is effected byheat and catalysts, for example, peroxides.

Theimpregnating cement can be applied to the fiber by any ofthe usualmethods suchias dipping in a solution ofcement, bythe application ioflatex, or"spraying, 'or spreading with a knife. The fabric tape,l whichcan be cut on the bias if desired, is wrapped about the reinforcingstrand which is usually a ste'el wire, but'itcan beany desired strand ofhigh tensile strength. Thus, I may use a heavy filament of plasticsuchas an extruded nylon wire or rod, ora hard-twisted cord of cotton, glassfiber, or other fibrous material. Other metals can also be employed forthe reinforcing strand, for example, aluminum'can be employed where itis desiredto keep down the weight of the construction. Itis desirable tocoat the mandrel before wrapping with a suitable release agent whichwill prevent the tape sticking to the mandrel and facilitate removal ofthe duct. Various materials are available for this purposek such assilicone resins, when rubber ,cementis employed. After curing, the ductis removed 'from thejma'ndrel by theapplication of air pressure andother well known methods o'fstripping. K

An import element in the manufacture of the improved duct is maintenanceof tension on thetape and the reinforcing strand during the curingoperation, thereby firmly bonding the layers of tape together as shownin Figures 2 6, which are sectional drawings of different methods ofassembling the duct. Thus, in Figure 2, the tape is shown wrapped aboutthe wire 13 starting from a point 14, passing under wire 15, thenclockwise about the wire 13 to a point 16. This, of course, is repeatedfor each winding, thereby providing four layers of tape For thispurpose, I may` 3 beneath the wire as shown, and making tween Athelayers .of fabric which yare ycompressed between the wires 13, 15, etc.and the mandrel underlying the tape. A thin layer of rubber or otherelastomer, 17, liesl next :to .the mandrel. and fllslthesp acesfbetweenthe-joints of the fabric and the mandrelg'asat' 18,1thus providing a'smoothy inner surface' forLthe 'duct-when vulcanized This layer orvlining 17 is 'usually formed frorn' thegc'ement which isapplied to thetape before Winding. 'l

The duct wall of Figure 2-is triple .plywith theedges bound beneath theadjacent reinforcing-strand, Lone edge passing beneath vtwo strands. 11nFigure T3, a double .ply construction isshown withloneedgel19 ofthe'tape locked and concealed between :two layers `of fabricbeneathreinforcing. wire 20. No seamtis' exposed onfthe outer surfacesof duct walls shown in Figures 2 and 3. Figure 4 shows a singleplyvconstruction with an external seam at.21.V y"When fwrapping, thetensionof the tapecausestit to hugthe wire `closely ,asshown at Y22. Theinternal surface layer 'is shown at\23.

The single ply wallfconstruction shown in Figures 4, and 6 are designed.for ducts with a highflexibility-requirement. The `,walls shown inFigures 5 and 6 expose no seam on the outside. Thus in Figure 5, theVfabric extends ,from 24 around ^wire 25, thence to edge 26 beneath wire27. `Inner liner ZS-completes the assembly.

In Figure 6, the edge 29 is concealed between Vtwo layers of fabric,while the long edge 30 passes beneath the adjacent wire strand 31 andabout half `way to the next strand 32, thus providing an'unusually wellbonded duct wall having the high exibility of a single ply construction.

Figure 1 shows a double pitch winding in which two strips of tape 33 and34 are Wound simultaneously. However, I usually prefer to employ asingle pitch winding,

applying a single strip of tape with enclosed reinforcing strand. Theends of the wire may be secured to the Wall of the duct in the mannershown in cci-pending lpatent application, Serial Number 297,046, nowPatentlNo. 2,697,452, December 21, 1954. I can alsoemploy `two or morestrands of reinforcing in a single tape, thus producing a duct withdouble, single, etc. pitch of the reinforcing strand. For rough service,VI can apply a wear strip to the outside of the duct to overlie thevreinforcing wire. This can be done on the finished duct, 4but forconvenience, it can best be applied before Vcuring while the duct is onthe mandrel. The wear strip can Vbe of harder, less exible fabric thanthat employed in'the body of the duct, -providing the edges of the `wearstrip are spaced apart sufficiently to allow free movement of theiwallofthe duct exposed between the reinforcing turns.

Where a soft end is desired on the duct, the reinforcing strand can beremoved near the Vend of the duct by slitting the layer. of Vfabricoverlying it. Thus, several turnsof wire can be removed at the end lof.the Ycornpleted, vulcanized duct to provide an end which can bestretched or expanded over a rigid'nipple and clamped on to provide atight, strong connection. A strip of bias tape an be applied to the areawhere the wire is removed. Other modifications will occur to thoseskilled in the art. In my improved duct construction, I have providedducting which can be made simply vand at lower cost than previouslywhile retaining the smooth bore for high velocity transmission offluids, particularly air and vother gases up to temperatures of 600 F.in the case of silicone impregnated glass fiber.

-Having `thus described my invention, what I claim is:

1. Areinforcediiexibleduct having -a spiral, inelastic reinforcingstrand completely enclosed in fabric tape having one free edge with saidreinforcing strand folded within the other edge, the windings of saidfabric tape forming said duct being spirally wound in the directionexposing said reinforcedV edge on the outside of said duct and cementedtogether without the free edge of said tape being visible on `theexternal surface of said duct.

2. The method of making a reinforced flexible duct which comprisesenclosing a stii reinforcing strand Within a fabric tape impregnatedwith a suitable cement, spirally wrapping said tape and strand on amandrel under tension sufficient to bind together the layers of fabricfirmly against the mandrel, the direction of the wrapping being suchthat the edge of the tape enclosing the reinforcing strand overlies thefree edge of the winding previously applied, thereafter curing theassembled Yduct on the mandrel while under said tension to effect aViirm bond between the-layers of fabric under the pressure applied bythe reinforcing, and finally removing the cured duct from the mandrel.

3. The method of making a reinforced exible duct which comprises foldinga reinforcing wire within a fabric tape impregnated with a rubbercement, thereby providing a winding strip having a wire enclosed at oneedge, spirally'wrapping said strip on a mandrel under tension sufficient`to bind together the layers of fabric by the pressure -eXerted by Vthesaid wire and said mandrel, wrapping said -strip on said mandrel in thedirection such that theedge of the strip enclosing the reinforcing wireoverlies the free edge of the winding previously applied,thereaftervulcanizing the assembled duct while on the mandrel withV-said wire under tension to elfect a rm bond between the layers offabric maintained under the pressure applied between the reinforcingvwire and the mandrel, and finally removing the cured duct from themandrel.

Y 4. The method of claim 3 wherein the winding strip is impregnatedYwith rubber cement before enclosing the reinforcing wire therein.

l 5. The method of claim 3 wherein the rubber cement employed issilicone rubber, and thefabric is of glass liber.

6. A flexible, reinforced, fabric duct having a smooth, cylindricalinterior, the walls thereof being formed of spirally Wound Vtapeenfolding a reinforcing strand in one edge thereof', the freeedge of thetape opposite said strand being bound'at each-turn `beneath the adjacentcoil of reinforcing strand,V adjacent coils being firmly cementedtogether with an elastic, rubberlike cement distributed betweenthe-layers of said spirally wound'tape, only that edge of saidjtapeenclosing said reinforcing strand being y visible on the externalsurface of said duct.

7. 'Ihe duct of claim 6 wherein one of said free edges of tape extendsbeneath two adjacent coils of reinforcing strand.

Y References cited in the ale of this patent UNITED sTATEs PATENTS

